A pump of said type has been described in U.S. Pat. No. 4,572,056 of the applicant. There it is stated that the pump head liner is to consist of chemically inert material such as the polymers polymonochlorotrifluoroethylene (KEL F) or polyvinylfluoride (PVDF). It is further stated that the pump head liner can also be made of ceramic material for example of aluminum oxide ceramic, which is a polycrystalline material.
The material proposed so far for pump head liners is not transparent and does not permit any view into the displacement chamber for a desired optical inspection of the displacement process. In addition to that, those sections of the pump head liner which are essential for observation are not visible from the outside, but are also covered by the pump head casing. It is particularly important to have the possibility of visual inspection since the delivery volumes of the pump type considered here, which has special application in the HPLC analysis techniques, covers the range of several ml/min to as little as a few microlitres/min and because there is, in addition, a trend towards a miniaturization with regard to the equipment and delivery rate capacity.